Well, Red and Yellow are perfectly fine colors for a Sea Wizard - ever saw the sun setting or rising upon the sea? The reddest red, and yellow, orange and purple as pure as you'll rarely see. But I think that his spells should look "wavy" or watery, like droplets of flame for example, with strange reflection like fire over a river.

That brings us back to "what's magic by the way ?" (since you mention "types" of magic)

Since magic is, by definition, something that is only limited by the rules of the game (and, well, if the game is, say Marvel Universe, these limits are going to be pretty far fetched ), I like to let every GM be the ruler of his own setting on this point, for obvious reasons.

Naturally. In my game I don't even get into that -it's abstracted out at far too high a level.

In my fiction (which was developed for stories, not games) I've created a magic framework to operate from that keeps magic use following consistent behavior, and more importantly, keeps behavior of characters using it consistent. Also prevents using it as a cheap plot device (usually a deus ex machina, akin to amazing pieces of technology seen only once in a Star Trek episode that never again makes an appearance).

As long as the reader feels the magic makes sense in the world you've created and the context it's used in it doesn't really matter what it is.

As an aside, interestingly enough, I've had a desire to run a Pathfinder or D&D E6 campaign because the magic in those settings gets so ridiculously over the top even by level 9. Once you hit 6th and 7th level spells it doesn't even make sense in the world anymore (or really, even past 3rd). But that's another conversation all together